I just went through the same thing... I needed 2 batteries.
As far as bang for the buck, EM3ev was the best deal.
The other bike has a 15" frame and is a very tight fit, The battery I bought from EM3ev would not fit... Luna was sold out, That left BafangUSA as my final source... it was perfect.
If shopping for quality, I would choose luna or EM3ev... I don't know about Bafang but luna and EMSev seem to take pride in their products.